Upper abdominal surgery causes respiratory muscle dysfunction. Multiple
factors have been implicated in the occurrence of such dysfunction;
however, the role of pain remains unclear. To elucidate the role of
pain, we studied 50 patients undergoing elective upper abdominal surgery
in a randomized, controlled investigation. Inspiratory and expiratory
muscle function were assessed through sniff mouth pressure (Psniff) and
maximal expiratory pressure (MEP), respectively. Pain during the
pressure maneuvers was assessed with a visual analog scale (VAS),
Measurements were made before surgery (Session 1), 24 h after surgery
(Session 2), and 1 h later, after intramuscular administration of
pethidine (analgesia group) or placebo (placebo group) (Session 3). To
evaluate the effect of pain, we used a mixed-effects model with random
intercept, having either Psniff or MEP as the dependent variable and
both surgical operation and the level of pain as fixed effects. Upper
abdominal surgery decreased Psniff in both the analgesia and placebo
groups (from 70 +/- 15 to 42 +/- 11 cm H2O [p < 0.05] in the analgesia
group, and from 69 +/- 15 to 42 +/- 10 cm H2O [p < 0.05] in the
placebo group). Intramuscular pethidine caused an increase in Psniff to
56 +/- 14 cm H2O (p < 0.05), whereas placebo had no effect. Pain
increased comparably after upper abdominal surgery in both groups (from
0.3 +/- 0.6 to 4.4 +/- 1.5) [p < 0.05] in the analgesia group and from
0.4 +/- 0.5 to 4.3 +/- 1.5 [p < 0.05] in the placebo group).
Intramuscular pethidine decreased pain as measured by VAS score to 2.1
+/- 1.0 (p < 0.05) in the analgesia group, whereas placebo had no
effect. Psniff had a statistically significant relationship to pain (p <
0.001). Adjusting for the occurrence of surgical operation did not
affect this result. MEP showed the same tendency as Psniff, but the
observed changes did not reach statistical significance. We conclude
that pain contributes to inspiratory muscle dysfunction after upper
abdominal surgery
